Thursday, October 22, 2009

60' Moth-A Preliminary Detailed Design Exploration

60' Moth-A Preliminary Detailed Design Exploration

Please read the whole thing if you're interested. I consulted with a naval architect on this and tried to be as detailed a possible. Questions and comments from those interested are encouraged.

60' MOTH-A Preliminary Detailed Design Exploration

I've long been convinced that the bi-foil revolution in dinghy design sparked by the Moth Foiler has potential for larger boats as well. The Out 95 guys in the UK and Sean Langman are also exploring this idea-among others. I decided to look at the numbers for a scaled up Moth just for the hell of it. I was surprised by the results.

I) The base boat: LOA- 12.75', SA- 86 sq.ft.;weight: 60lb.hull + 150 lb. crew =210lb.s all up.
II) Scaling up:
*A) Sail Area-Since sail area varies as the square of length I squared 12.75(162.5) and squared 60(3600). Then I divided 3600 by 162.5 and multiplied the result by 86(Moth SA) . So the scaled up SA=1905sq.ft.----------------------- ****
Weight- Weight/displacement varies as the cube of the length. So I cubed 12.75 (2072.67) and cubed 60(216000).Then I divided 216000 by 2072.67 and multiplied the result by 210(Moth sailing weight). So the weight of the scaled up boat is 21,884 lb.'s.----------
III) Analysis/judgement calls- The most surprising thing when I was first doodling with these figures is the weight. At almost 22,000 pounds the scaled up Moth was way heavy by comparison to an ORMA 60 trimaran(12,000lb.'s) and to L'hydroptere(11,975lb.'s). But the defining characteristic of the Moth above all else is that it is a MONOHULL. So to preserve that characteristic at this length I decided that it would be important that the boat was selfrighting like any other(hopefully) 60'monohull. The "weight budget" certainly would allow that.
NOTE:VERY IMPORTANT: the resulting 60'monofoiler IS NOT, REPEAT NOT a scaled up Moth as a carefull reading of this Design Exploration will reveal.
This Design Exploration reveals that while this self-righting 60' monohull foiler is possible and has speed potential AT LEAST equal to the ORMA foil assist trimarans it is nonetheless on the leadingedge of what is possible today.

So this is what I came up with after playing with the numbers for some time and running the whole thing by a friend who is a naval architect:
60' MONOFOILER-----------------------------
2) Target Beam 50'-increase from scaled up Moth; about same proportion as aeroSKIFF 14(see post#15 Peoples Foiler Thread)
3)Target SA: 2500 sq.ft.-increase from scaled up
4)Target Minimum all up sailing weight including 5231 lb.s on an 18' 60° canting strut: 14,731lb.'s.--------------------------------
5) Target boat weight w/o canting keel ballast:
6) Maximum additional ballast: 3771 lb.'s water ballast in a sliding tank-perhaps sliding within forward cross beam or just aft of beam. Tank is filled while over hull to limit weight of plumbing requirements. approx. dimensions: 1.5' X 6' X 6.4'. Possible fore and aft ballast sliding system .----------------------------------------
7) Weight with maximum ballast:18502lb.'s(plus 2-4 crew)
-SA 2500sq.ft.----------------------------------- -Displacement:
14,731lb.'s ; Max: 18502---
-Draft(off foils) max
30 sq.ft. main foil; 15 sq.ft rudder
D/L ratio- 60' Monofoiler: 30.4--------------- D/L ratio- Orma 60/L'hydroptere: 24.8------
Bruce Number-60' Monofoiler: 2.03---------
Bruce Number-ORMA Tri: 2.39--------------
Bruce Number-L'hydroptere:2.65------------
(Bruce number is the sq.rt .of SA divided by the cube root of displacement)----------- --------- For what it's worth, the following comparison is between the 60'Monofoiler and the 60'ORMA trimaran.And I consider it one of the most important comparisons of all. The ORMA trimaran is presumed to have 60% of it's displacement supported by a "banana foil", with 30% of it's weight supported by the ama while flying the main hull. For this comparison the 60'Monofoiler is presumed to be flying on just two foils. The vertical fins of neither boat are included and both sides of the foils are included:
1)Orma 60-estimated ama wetted surface 124 sq.ft; estimated foil wetted surface 32 sq.ft.(both sides) Total 156 sq.ft. Now this figure is divided into SA(3000sq.ft.) giving 19 sq.ft. of SA per sq.ft.of wetted surface.
2) 60'Monofoiler Mainfoil area(both sides): 60sq.ft..Rudder foil area(both sides) 30sq.ft.. Total is 90 sq.ft . Dividing SA(2500sq.ft.) by this figure gives 27.7 sq.ft. of SA per sq.ft. of wetted surface.
**Notes and Design Considerations
( see below for "More notes..." including lift calculations, foil
loading and more)
A) The number one design consideration for this boat was that it was self righting and that it would qualify as a monohull under any rule. Therefore it does not have buoyancy pods that in any way resemble or that could function like a hull-simple rectangular spaces at the maximum beam supported by carbon cross tubes. These buoyancy tanks in combination with the 18' 5000+lb. 60° canting bulb would prevent capsize and or right the boat from a knockdown. The weight in the bulb was specifically chosen to be 1.5 times what would be required to right the boat from a pitchpole. The canting keel could be explored a lot since it is relatively light for a 60 footer(5200+lb.'s). It would be ideal for it to be clear of the water when the boat is foiling-at least above 20 knots.
When an Orma tri fly's the main hull it does so with about 2lb. per sq.ft. of windpressure on 3000 sq.ft. of sail. The 60'Monofoiler with max ballast can sail with it's maximum SA in about the same pressure. And in lighter conditions it can ditch up to 3700+ lb.'s of water ballast facilitating relatively light air take off in an 9-12 knot wind.------------------------------
(see Righting Moment below)
Preliminary conclusions:
It appears to me that the 60' monofoiler could be built but right at the top end of available technology.It would be likely to equal a multi of it's own size that did not use foils and appears to have more SA per sq.ft. of wetted surface than even an ORMA tri though especially in light air the ORMA would be faster since it can retract it's hydrofoil . The concept of an extremely fast selfrighting hydrofoil holds a lot of promise.
More notes and references:
1) Righting Moment---------------------------
When off the foils the heeling arm (CE-CLR) is 43'. When on foils it is 51.75' . Hull bottom clearance to water is 10.75'. On foils max draft ,level,is 5'.
This boat is a monofoiler and as such will be sailed heeled to weather 15° at maximum righting moment.
Elements of Righting Moment:
A) rig CG is approximately at the
CE; 1460lb. @ 14.5' to weather= 21,
B)canting bulb- 5,231lb.'s at 60°( 15.6') +
3' weather heel =5231 X 18.6'= 97,296 ft. lb.'s.
C)Hull 8040 X 5'to weather= 40,
D)rack(deck) ballast 23' = 6' to weather
=29 X 3771= 109,359 ft. pounds
MAXIMUM RIGHTING MOMENT= 268,025 ft. lb.'s (A+B+C+D above)
MAXIMUM PRESSURE WITH 2500sq.ft.(268,025 divided by 51.75=5179. Divide 5179 by 2500(SA) = 2.07 lb.
2) The 50' beam could be one "wing" but would probably work better as two beams supporting a fixed empty "tank" at each end for buoyancy. A small tank containing up to 3770 pounds of water will also slide across the forward beam or just behind it. For the sake of getting the boat defined as a monohull based on whatever rule the buoyancy would not look like or function like a hull while normally sailing. In the event of a knockdown it would help to right the boat. I've talked with Alex of the OUT 95 project and he says their solution(ultra narrow hull with very wide wings on a 32 footer) is legal under the rules. Exactly which rules he was referring to I'm not exacly sure.
********The hydrofoils on this 60' monofoiler are in the hull : one mounted on the daggerboard and one mounted on the rudder.They might be partially retractable in non foiling conditions. No foils on the end of the wings.The canting keel strut would be behind the daggerboard.(Like Maximus among others)
3) The canting strut is right on the edge of feasibility. But it probably can work: its half the weight of a VO 70 bulb but half again as long.Based on the fact that the load is 81% of the load on a Vo70 the engine hp required is likely to be about 23hp(vs 29 for the Volvo).
The Volvo 70 has a max speed so far of 40.6 knots according to Sail mag-just 5 knots short of the top end(so far) of a G Class cat(100+')-same source. And ,as I understand it, they peg the keel max out in fast conditions.
The Farr design #550 Volvo 70 has a strut approximately 12-13' long with 9920 pounds in the bulb with a variable displacement from 27,558 to 30,865lb.'s. The monofoiler as stated above needs 5200+lb.'s at 18' to be self rightng.
******I don't think that the bulb/strut being offset will have too much negative effect when you consider that L'hydroptere maintains control at over 40 knots with most of the drag coming from a foil 20' to leeward using a centerline rudder. I think that it would be important on the monofoiler to figure out a way to get the canting strut and bulb out of the water over 20 knots-keeping in mind that it will probably be sailed upwind with windward heel like the Moth. The Volvo has a max cant angle of 40°, the Schock 40 and Max Z86's 55° and a 26 footer from Bethwaite 60°.
**This area would need plenty of research and testing. It is ripe for some sort of unique solution....
4) Bruce numbers- I calculated the Bruce number for L'hydroptere from information on Sail Area given in Sail mag.. But looking at the head-on picture and using a scale ruler I'll bet they can't carry that area(3700sq.ft.) in the same pressure that an Orma tri can carry it's 3000sq. ft. The monofoiler can carry it's maximum sail area in the same pressure an Orma tri can carry it's maximum sail area. Regardless of it's actual SA for a given pressure a well designed multifoiler will be faster than the 60 monofoiler any day. But the monofoiler and ORMA even using "foil assist" will be closer.And a "conventional" multi sailing only on it's hulls(even flying the main hull with no foil assist) would be still closer in speed to the monofoiler-with the monofoiler probably having a significant edge.
**I 'm leaning toward believing that the Bruce Number or Bethwaites "SCP Divided By Total Weight Ratio" may not be good comparitive numbers when comparing an all out foiler to a "foil assist" boat like the Orma. **When you look at these Bruce Numbers you may see what I mean: Moth 1.56 ; A Class Cat 1.82 ; 49er 1.76 ; IC 1.58 . All the boats shown show a Bruce number indicating they should be faster than a Moth-and they are when it is not foiling. But when on foils the Moth beats every one of these boats. So I'm leaning toward SA/wetted surface as a possible way to compare the boats when at least one of them is a foiler. In my comparison of the 60' monofoiler to the ORMA I showed that even though the foiler was heavier it had more power applied to less wetted area than did the ORMA. Of course ,this is simplistic: it didn't take into account induced drag of the foils, the vertical fins or the wavemakng resistance of the partially submerged ORMA ama. Nonetheless, it seems like a good indicator....
5) Foil Loading- The 60' monofoiler will have foil loadings with and with out the sliding deck ballast. For takefoff(see #5 for lift/speed calculations) it has a foil loading of 392.8 pounds per sq.ft . That is based on 80% of the total dispacement of 14731 which equals 11784 divided by 30 sq.ft.. Above 20 knots ,at some point, it will add additional ballast and have a foil loading of 493 pounds at a displacement of 18502lb.. Most foilers are designed with about 80%(or so) of the load on the forward foil and loading is calculated based on the area of one side.
****For comparision the foil loading of the ORMA tri with and estimated banana foil area of 16sq.ft. is 450lb. per sq.ft. at a displacement of .6 X 12000=7200. A Rave foiler sailing in 2lb. of pressure has a mainfoil(2) loading of 356lb. per sq. ft. (develops RM using the foils increasing loading well past this number at max pressure). A Moth has a mainfoil loading of 169 lb.per sq.ft.-and only changes with different crew weight. And the first two person monofoiler to fly-David Lugg's I14 had an approx. mainfoil loading of over 500 pounds per sq.ft. (small "high speed" foils), if I remember correctly.
L'hydroptere has surface piercing foils and basically starts out with low loading and high wetted surface(56 sq.ft.est.) and ends up with high loading and low wetted surface(14 sq.ft.est.). The picture of L'hydroptere in Sail shows it sailing on one of two main foils at an area I estimate to be 7 sq.ft. for a loading of 1368lb per sq.ft.(.8 X 11975 divided by 7). I'm guestimating that that picture was taken when the boat momentarily flew a foil and that a more realistic loading would be based on 14 sq.ft.(7sq. ft. per main foil) for a realistic loading of 684 lb.'s per sq.ft. At takeoff with 56 sq. ft. of foil area loading is 171lb.sq. ft. but the loading rapidly increases whereas it does not change on a monofoiler unless ballast is added.
Additional Notes: Using this formula for lift: Area=Weight divided by(the factor 2.09 X speed in mph² X Cl(coeficient of lift) along with my copy of Theory of Wing Sections and the information there on the 63412 section(p522 &523) I came up with the following for the monofoiler:
Light displacement =14731 .8=11784------
Heavy Displacement=18502 X .8=
Mainfoil area 30 sq.ft.--------------------------
1) The boat will lift off at a boat speed of 12 mph(10.4 knots) with a CL of 1.3. This is outside the drag bucket(but way below stall) but ,of course ,as soon as the boat lifts off it will accelerate.Moths, using this foil, lift off at even higher CL's.--------------------------------
2) At a boat speed of 16mph(13.9 knots) the CL drops to .73-just inside the "drag bucket" for this foil.-----------------------------
3)At 23 mph(20 knots) after the additional ballast is added the CL is .44-well within the drag bucket. The additional ballast may not all be added at once but I checked it at the minimum speed for which some ballast would be added.
A personal note: I'm not at all convinced that sailing foilers are a good idea for ocean racing until the electronic systems are developed to spot partially submerged objects in time to avoid them. L'hydroptere was stopped by just this kind of thing. I think all high performance boats would benefit from this kind of equipment and I imagine it's not too far away or may be already available for all I know. In fact according to the L'Hydroptere site they are experimenting with this kind of technology...

Tuesday, October 20, 2009

three boats in one

I've started my second monohull foiler platform that will actually be three boats in one. The idea is to have a basic platform with interchangeable parts that will allow a 22' foiler, a 22' trimaran with planing amas and a 22' Trapwing experimental movable ballast boat.

All these variations use foils to one degree or another and the plan is to get the hardware built and be able to spend huge amounts of time sailing instead of building.

I should have a whole lot of fun and learn a lot over the next five years while I explore these ideas.

Thanks to my experience with Dr. Bradfield I've sailed a Rave a lot and coupled with the limited foiling on my own 16 footer I can tell you that foiling is one of the most thrilling things you can do on the water! Try it on any boat you can.

And keep in mind these are early days in the bi-foiler revolution-don't buy into the "its too hard" bull or that crap about having to walk a foiler out to deep water. The newer boats will be much more user friendly and yes,it is a revolution!

Thursday, October 15, 2009

the latest design using a Blade F16 hull

LOA 16' using a Blade F16 hull from Matt McDonald of Falcon,LLC in Port Canaveral, Fl.and:
Hull weight(with cockpit) 73lb(actual weight+ cockppit mod)
SA 160 sq. unstayed squaretop rig,carbon mast- 35lb
Foils-17lb (foil assist approx 70% lift depending on crew weight)
12' wing,all up-20lb
movable ballast-160 lb
motor,controls,battery (25lb est)

SUB Total=330lb (405lb for Turbo self-righting version with fixed 75lb ballast in bulb integrated with "foil assist"foils)
TOTAL = 510lb
160@ 9'
20 @ 4' =


HM@ 1lb/sq.ft. pressure = 1600

This is with crew contributing virtually nothing to RM. A side seat option allows the crew to sit slightly outboard but still in a relatively fixed position-for ablebodied crew only and it adds RM.
There is no guarantee that even after testing the skinny hull turbo version will be suitable for disabled sailors-only extensive testing will prove whether or not that is possible. IF that is possible it REQUIRES the selfrighting option.

This thing will trailer with the wing pivoted fore and aft and will require the same room a WETA tri does to launch rigged at a launch ramp. In Florida the boat would launch using a dolly like a cat does and that will make it easy. Keep in mind how heavy the 2.4 meter is and it is successfully launched in many areas. This boat is much lighter than that-maybe about the same as a Bongo-and about the same as a Hobie 16. Launching will be no problem with a dolly on a beach and if the ramp is wide enough the boat can be launched right off the trailer.


The lead in the cart that slides athwhartship will be in approx. 20lb segments an will be REMOVABLE. There is no reason to sail with max ballast on a light day.

A production version would have a reefable rig.

This version will not be the first version which will be my 22 footer which is being worked on now. It will be done as soon as possible.

Additions include front twin 50 cals so any one who claims I am not a sailing vessel can eat my lead

Saturday, October 10, 2009


Heres a new rendering of my new favourite bi-foiler the KissKut.

Here are the numbers:

LOA 4.5 m=14.7'
Beam 4.5m=14.7'
SA=9sq.m=97 sq.ft
weight est.=40kg=88lb.
Price-an amazing(!) $42,000US no peoples foiler if this price is accurate.

I see some problems with veel heel-if anybody else does and can articulate it I'd sure like to know. Appears I have the wing angle slightly too low-that means max veel heel would be greater than this while maintaining the same clearance between buoyancy pod and water as between hull and water. I still don't like the twin vertical struts or the 7'(est) long main foil. A couple of things are immediately obvious: there is too much mainfoil area* and along with the twin struts that results in a drastic increase in wetted surface with veal heel when keeping the leeward tip the proper distance below the surface.

* estimated 3.5 sq. ft.; foil loading with 320lb crew=93lb/sq.ft. Moth foil loading=160lb.per sq.ft. approx. This foil could be shortened to approx. 4' with a 6" chord. and ha
ve the same foil loading as a Moth and that is with TWO people on board KissKut. That would help everything... but it would be even better when jumped with manual control and dual midship wands.

Some mothies think it won't work. To that I say horsepetunias

Wednesday, October 7, 2009

Questions and answers

1) Do you think that a bi-foiler could be designed to be significantly easier to sail than a Moth?
Technically a moth is a sub category of bi-foiler, so, logically speaking, the question is do I think that a bi-foiler can be faster than a bi-foiler, ergo if we apply the atlernative, can a moth be designed to be faster than a bi-foiler. well no because it is one, so then the question becomes can a moth be faster than a moth, well yes a moth can be designed to be faster than a moth, however by definiton it is a moth, so it can't be. In summary, a bi-foiler cannot be designed to be faster than itself.

2) Do you think a forward wand position is critical or could a midship or aft wand could have some potential?
the forward positioning of the wand is absolutley critical. If the wand is not held tightly then an expelleramus spell will easliy disengage the wand from your hand. Storing the wand aft could solve this issue however it would impact the wand users ability to cast spells.

3) Do you see any potential value in a control system that links the movement of the mainfoil flap and rudder foil flap(or rudderfoil angle of incidence) together in an adjustable(mixable) way?
I think that any system that links the two foils together, say using some 2" x 1" tiber) into a single, unified foil would cause an excessive amount of drag as it is pulled through the water under the boat, so no. I like the idea of the mix tape though.

4) Do you think a bi-foiler could be faster if altitude was controlled manually(no wand)-even if it took lots of practice to get it right?
Well spell casting does take a lot of practice to get things right, and you can cast faster if your attitude is done manually.

5) Do you think in some future time the idea of intentionally jumping a bi-foiler(not necessarily a Moth) would be feasible-or catch on if it could be done safely, repeatedly?
Jumping is fiesable and necessary. When trying to escape persuit from the Hazzard county sherrif, jumping over the nearest river with a washed out bridge into the next county has shown to be able to be done every week for a number of years.

6) Do you think a keelboat, with the right numbers, could ever foil?
Didn't that Americas cup boat America II have a foil winged keely thing, so YES.

7) Where do you see bi-foiler development,outside the Moth Class, heading?
I think that bi-folding chairs were well developed before the moth class ever came along.

9) What is your opinion on a variable geometry main foil-a foil design where the area could be reduced under sail(or increased for that matter)?
I am sorry, I didn't pass geometry at school and will have to pass on this one.

10) What is your opinion of adding wand+flap altitude control to a surface piercing foilers main foils?
I don't have any surface piercings, as my mother won't let me get them, she says they will make me look cheap.

11) What do you think of adding buoyancy pods -a bit larger than the ones on current foilers- to help make it easier to learn to sail a monofoiler?
Why do we need bouyancy if the boat doesn't touch the water??

12) Did you know that several top Rave(16' multifoiler) sailors modified their boats to MANUAL altitude, MANUAL FOIL RM(roll) and MANUAL PITCH control which proved faster in racing-replacing the existing wand system?
I haven't been to a rave in years. At the last one I met a girl called Jenny who sold me a foil, she turned out to be a real mighty bitch, so I think that is what you mean, not manual pitch.

13) What is your opinion of adopting the "shared lift" concept first pioneered in the ARC 21 cat (and now with Mirabaud) to allow a longer foil "footprint" for a given size monofoiler?
Well I think it is a good idea that people use the shared lift concept. It reduces green house emissions as there are less cars on the road whihc reduces your footprint.

14) What effect do you think changing the planform and aspect ratio of the Rush foilboard(air chair derivitive) foils would have on speed, jumping, and "ease" of sailing a foilboard?
I think that changing the plan and form of the asphalt patio is a great idea. I don't think that rusing forward in to a chair delivery is a smart thingm less speed and reducing the urge to jump in will make things easier.